6-chloro-3,4-dihydro-2H-1,2,4-benzotiadiazine-7-sulfonamide-1,1-dioxide known as hydrochlorothiazide and abbreviated HCT has been long used as an active pharmaceutical ingredient to treat hypertension. Telmisartan in acidic form or as an alkali, preferably sodium, salt is another active pharmaceutical ingredient and may be used as an angiotenzin II antagonist. Chemically telmisartan is a 2-[4-[[4-methyl-6-(1-methylbenzoimidazol-2-yl)-2-propyl-benzoimidazol-1-yl]methyl]phenyl]benzoic acid. Telmisartan itself is at neutral pH poorly soluble. That is, it does not dissolve more than 2 μg per ml of pH 6.8 phosphate buffer. In order to increase its bioavailability, it is normally administered as an alkaline salt, such as sodium salt or incorporated into a composition which itself provides for an alkaline pH. It is advantageous to administer both drugs concomitantly or even more to manufacture a composition comprising both to treat hypertension. Such composition is known from WO 03/059327, however specific technology was used therein to prevent the degradation of hydrochlorothiazide which inevitably occurs when this substance is exposed to alkaline media. The main degradation product of hydrochlorothiazide is 4-amino-6-chloro-1,3-benzenedisulfonamide (DSA).
By providing said hydrochlorothiazide and another alkaline active substance, in separate units, a stable pharmaceutical composition could be prepared. Separating hydrochlorothiazide, which degrades under alkaline conditions from another alkaline active substance requires special pharmaceutical composition manufacturing machinery. Additional difficulty represents the fact, that both active substances need to be released from the composition substantially concomitantly.